The present invention relates to internal combustion engines, and, more particularly, to internal combustion engines with an exhaust gas recirculation system.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey) issued on Sep. 8, 1998, which is assigned to the assignee of the present invention.
Exhaust gas recirculation (EGR) is very effective in reducing NOx from a diesel engine, but it also tends to increase particulate matter (PM) emissions. In order to maximize the NOx reduction, a common practice is to apply as much EGR as possible to the engine in certain regions of the engine operating map with an acceptable increase in particulate matter. Additionally, the recent emission regulations mandate emission compliance under all ambient conditions. These requirements make EGR rate control important to the viability of EGR technology.
An air mass-flow sensor has been used in some engine applications to provide feed back signals for EGR control. However, the accuracy of the current generation of air mass-flow sensors is not accurate enough to meet the EGR control requirements for the heavy duty truck diesel engines. Oxygen sensors are more accurate, but their transient response is not fast enough for feedback control of the EGR rate. In addition, the current generation of these two types of sensors do not meet the durability and reliability requirements of the heavy duty diesel applications.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an exhaust gas recirculation rate control system adapted to be fluidly connected to an exhaust manifold and an intake manifold of an internal combustion engine is provided with a plurality of critical-flow nozzles, each critical-flow nozzle having an intake end and an output end, the intake ends being adapted to receive the flow of exhaust gas. At least one valve is provided, with each valve being fluidly coupled with at least one output end, and a control module operatively connected to each valve for controlling exhaust gas flow therethrough.
In another aspect of the invention, an internal combustion engine is provided with an intake manifold, an exhaust manifold and an exhaust gas recirculation rate control system fluidly connected to the exhaust manifold and to the intake manifold. The exhaust gas recirculation rate control system includes at least two critical-flow nozzles, each critical-flow nozzle having an intake end and output end, the intake ends being fluidly coupled to the exhaust manifold; at least one valve, each valve being fluidly coupled with at least one output end; and a control module operatively connected to each valve for controlling exhaust gas flow therethrough.
In yet a further aspect of the invention, a method of controlling a rate of recirculation of an exhaust gas in an exhaust gas recirculation system is provided and includes the steps of providing at least two critical-flow nozzles, each critical-flow nozzle having an intake end and output end; fluidly coupling the intake ends with an exhaust manifold of an internal combustion engine; fluidly coupling at least one valve with at least one corresponding output end and with an intake manifold of the internal combustion engine; operatively connecting a control module to each valve; directing the flow of the exhaust gas into the intake ends; and controlling the amount of the exhaust gas released through each valve.